With the technology foundation of the solid state lighting, some lighting facilities have been produced for daily and landscape uses as well as high power lighting facilities for industrial uses. These lighting facilities have a somewhat lower color temperature, T≦3500K, falling into the category of warm white lighting. If the color temperature is higher, T>4600K, the semiconductor facilities will be categorized as cold white light.
The first red phosphor powder is a Lepard phosphor powder with a formula of MeIIS:Eu+2, wherein MeII is equal to Ca+2, Sr+2, or Ba+2. The second type of phosphor powder is the compound of AIIBIV wherein AII=Zn, Cd and BIV=S, Se, Te or their inter-soluble compounds, for example, (ZnS)0.4(CdS)0.6. Ag. The application of these phosphor powders are now very limited because (1) MeII S sulphide is low in chemical stability and readily decomposed in air, and (2) AIIBIV compound contains cadmium, which is a strong toxin.
In 1965, the first rare earth phosphor powder was developed with a vanadic acid, (Y,Eu)1VO4, as its substrate (please refer to Handbook of Phosphors Press NY, 1999). The red phosphor powder has been produced in batches. The excited wavelength of the near ultraviolet of the phosphor powder is λ=365 nm. Since the phosphor powder has a good quality and high performance, it has been widely applied.
It was followed by the development of oxide phosphor powder: Y2O3:Eu or Gd2O3:Eu, with an excited ultraviolet wavelength of λ=254 nm. Since the stability and performance of the phosphor powder are very high, it is still now used in the light sources with η=50 lumen/watt. Later, the invention of sulphur oxide phosphor powder with a formula of (ΣLn)2O2S, wherein ΣLn=Y, La, Gd, Eu, Tb, Sm. Based on the sulfur oxide phosphor powder, new cathode phosphor powder, X-ray phosphor powder, and laser phosphor powder were invented (please refer to the Russian Patent No. 1603763 by N. P. Soschin et al., Dec. 1, 1988). Although widely used, the red phosphor powder based on Yttrium (Y)-Lanthanum (La)-Gadolinium (Gd)-Europium (Eu) sulfide has a substantive drawback: the red light with wavelength λ=616, 626, and 708 nm can only be excited to luminesce at the near-ultra violet subband of wavelength λ=365˜405 nm. Therefore, the phosphor powder can only be applied in the semiconductor light source of λ=395 nm, and not suitable to be excited by the blue-light semiconductor heterojunction. The drawbacks of this phosphor powder based on (Y,Eu)2O2S has been described in the Russian Patent No. 2064482 please refer to the Russian Patent No. 2064482 by N. P. Soschin et al., Apr. 18, 1991).
People later tried to develop phosphor powder which can be excited by blue light heterojunction to emit red light. A series of articles concerning the new oxide phosphor powder, CaSiAlN3:Ce (please refer to Hanz Luo Jiang et al and Materials Science and Engineering MSB 115118) details these experiments taken. However, the production of material CaSiAlN3:Ce is very complicated because of its low light output and high cost.
The present inventors of the present invention have recently attempted to make the phosphor powder Sr5Al2O8:Eu+3 disclosed in a newly published patent as sample (please refer to N. P. Soschin, high-powder white light semiconductor). Nevertheless, the inventors of the patent did not clarify the exact composition of the phosphor powder when detailing the synthetic process, nor specify the realizable oxidation state of the main exciting agent Eu+3. Also, the inventors did not specify the crystal structure of the compound and the concentration ratio of SrO and Al2O3, which are drawbacks demanding improvement.